Hi Hamed, generally for producing well adhered layers of these metals, you are best first depositing a very thin layer (around 1nm or so) of fresh metal oxide such as that of Zinc, aluminium or titanium. You may also find an alternative is to "activate" / clean the surface of the plastic in the system, prior to deposition by ion / plasma cleaning or bombardment. Though I have not used many different polymers myself PET is most often the choice for vacuum deposition and is economical, Capton is another more expensive specialised material, but can cope with higher temperatures, many other polymers tend to have high vapour pressures and out-gas under high vacuum, so are not ideal.

Hi Hamed, just a guess here but since gold and thiol (S-H) groups have a strong attraction for one another, a polymer with hanging S-H groups would work well. You could even take natural rubber and try to reactively modify the surface with pentaerythritol tetrathiol to make it more adhesive to gold and silver.

Thank you for the comments.

Hi Phil, can I use PETG instead of PET? My substrate is about 5 mm thick an I want it to be clear. It seems that clear PET sheet with this thickness is not very well commercially available. PETG, however, is available in different thickness.